Optical computing is recognized as an emerging technology. Its continued maturation depends heavily on the availability of a wide range of logic devices and, more specifically, optical devices performing combinatorial logic functions. While the range of combinatorial logic functions such as AND, OR and NOT is important in the first instance, it is almost equally important to provide cascadability, logic level restoration, phase insensitivity, speed and input/output isolation. An additional consideration, though not presently decided upon, may be a need for an all-optical device.
All-optical, cascadable soliton logic devices have recently been demonstrated in birefringent optical fiber to provide several picojoule switching energy and a fan-out of six. See, for example, Opt. Lett., Vol. 15, pp. 417 et seq. (1990). Logic outputs for this family of logic devices are presented according to a time-shift-keying criterion. That is, a logical "1" corresponds to the occurrence of a control pulse within a desired time slot or sampling interval, whereas a logical "0" corresponds to the substantial absence of the pulse during the desired time slot or sampling interval. Logic operations are performed by slowing or "time-shifting" the control pulse through interactions with a signal pulse within the birefringent optical fiber. The interactions produce a soliton dragging effect.